Intake manifold technology has evolved constantly throughout the history of the automobile industry. Even though the intake phenomenon, which is a rather complex and dynamic event, is relatively well understood as a result of computer modeling efforts of the last twenty-five years, designing an intake manifold for a specific engine and vehicle application remains an exceedingly difficult task. It is simple to design a manifold for a engine which runs at one speed where there is no engine compartment space limitations. However, in the real world where engines must fit within relatively small engine compartments and the engine needs to operate throughout a wide speed range, manifold design becomes a series of difficult compromises.
The concept of manifold tuning is well known. It is possible to select plenum volume, an intake manifold runner length, and a cross-sectional area so that the frequency of the pressure wave within the runner optimizes the pressure at the intake port when the intake valve is open. Tuned manifolds are designed to optimize performance within a selected engine speed band. Frequently, tuned intake manifolds will actually hinder engine performance when operated substantially outside of the selected band such as in extremely low engine speeds or very high engine speeds. As a result of efforts to improve fuel economy, smaller and smaller engines are being utilized today and there is a renewed interest in improving engine wide-open throttle performance.
The interest in ram-tube manifolds appeared to peak in the 1960's when they were used extensively on high performance race cars. Examples of early ram-tube induction systems are illustrated in U.S. Pat. Nos. 2,845,911; 2,927,564; and 3,303,832. As illustrated in the Platner U.S. Pat. No. 3,303,832, a ridiculously large manifold by modern standards was used in order to achieve sufficient runner length and to maintain uniform runner-to-runner flow characteristics to optimize performance at a selected engine operating speed range.
The problem facing designers today is to optimize engine performance within the confines of a very small engine compartment. It is also necessary to design a manifold which is as simple as possible so that it can be manufactured cost effectively while maintaining manifold weight to a minimum.
Examples of more recent ram-tube intake manifolds are illustrated in U.S. Pat. Nos. 4,440,120 to Butler; 4,643,138 to Ruf et al; 4,643,137 to Choushi et al; and 4,669,428 to Ichida et al. In order to achieve a long runner length and a compact manifold, the Butler and Ruf et al patents disclose a manifold which utilized runners which extend generally helically about a longitudinal axis above and parallel to the crankshaft axis in a V-type engine. The Ichida patent utilizes a variable length intake runner manifold design in which the intake manifold extends a very significant distance in front of the engine to obtain suitable runner length without becoming excessively high.
The Choushi et al patent utilizes a central plenum between and raised above the engine in which a plurality of generally J-shaped runners extend out each side of the elongated plenum and cross over to connect to the intake port on the opposite side of the engine in a criss-cross manner.
It is an object of the present invention to provide a ram-tube intake manifold which has a minimal height and length in order to compactly fit on top of the engine so as to fit within small engine compartments.
Another feature of the present invention to provide equal length and cross-sectional area runners having the minimal uniform flow resistance which achieves the optimal tuning effect in the selected engine operating speed range.
These and other advantages and features of the present invention are described in the accompanying specification and drawings.